Merge: Attribute and autoinit annotations

A big set of loosely coupled but related changed on the annotations on attributes and methods.
Here is a summary of the changes on the user-side:

* No more special case for the kind of classes, so you can use `autoinit` in interfaces.
* Explicit annotation `autoinit` is understood on attributes and is the default on value-less concrete attribute.
* Abstract attributes are `noautoinit` by default, if `autoinit` is given, it is applied on the setter. This way abstract attributes are basically just a couple of getter-setter. close #1311

This way there is less special cases and behaviors. Still more work is required to finish #1322.

Pull-Request: #1433
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc src/compiler/abstract_compiler.nit
Simple merge

diff --cc src/rapid_type_analysis.nit
Simple merge

diff --cc src/semantize/typing.nit
Simple merge